A. El-Brashy

Fluorimetric determination of some thiol compounds in their dosage forms

A simple fluorimetric procedure was adopted for determination of three pharmaceutical compounds containing thiol groups namely, captopril, D-penicillamine and N-acetylcysteine. In this method, the drugs are treated with 1,2-naphthoquinone-4-sulfonic acid. The latter is reduced to 1,2-dihydroxynaphthalene-4-sulfonic acid which has a maximum fluorescence intensity at 480/318 nm (lambdaEm/Ex). The method is sensitive to 0.5-4.5 pg ml(- 1) with minimum detectability 0.05 microg ml(-1) (S/N = 2), and has been applied to determine these three thiols in their dosage forms. The results obtained are compared favourably with those obtained by their pharmacopeial methods.

Colorimetric and titrimetric assay of isoniazid

Two methods are proposed for the determination of isoniazid in pure form or in tablets. In the first method chlorpromazine hydrochloride, when treated with 2-iodoxybenzoic acid as an oxidant in 50% w/v o-phosphoric acid solution, is oxidized to chlorpromazine free radical which absorbs at 530 nm. The red free radical is readily reduced quantitatively by isoniazid to the colourless chloropromazine. The addition of isoniazid to a red solution of chlorpromazine free radical results in a decrease in absorbance in direct proportion to the quantity of isoniazid. This forms the basis for the quantitative determination of micro-quantities of isoniazid (3-18 micrograms ml-1). The second method involves the titrimetric determination of isoniazid using N-bromophthalimide as a titrant. The end-point is determined either directly using methyl red or amaranth as indicator, or by a back titration method in which a known excess of N-bromophthalimide solution is added to isoniazid solution and then the residual unreacted reagent is determined iodometrically. The results by the proposed procedures were in good agreement with those obtained by the official methods.

Stability‐Indicating HPLC Method for the Determination of Quetiapine: Application to Tablets and Human Plasma

Abstract A stability‐indicating reversed‐phase high performance liquid chromatographic method was developed for the analysis of the antipsychotic drug quetiapine. Quetiapine was determined in presence of two of its degradation products; quetiapine N‐oxide and quetiapine lactam. The analysis was carried out using a 250 mm×4.6 mm i.d., 5 µm particle size Zorbax SB‐Phenyl column. Mobile phase containing a mixture of acetonitrile and 0.02 M phosphate buffer (50∶50) at pH=5.5 was pumped at a flow rate of 1 mL/min with UV detection at 254 nm. The method showed good linearity in the range of 0.08–20 µg/mL with limit of detection (S/N=3) 0.03 µg/mL (3.3×10−8 M). The suggested method was successfully applied for the analysis of quetiapine in bulk, tablets, and human plasma with average recoveries of 99.96±1.25%, 101.37±0.481%, and 100.82±1.53%, respectively. The proposed method was also applied for the determination of quetiapine in the presence of some co‐administered drugs as clomipramine, carbamazepine, and fluconazole.

Colorimetric Determination of Some Important Hydrazine Derivatives

A simple and rapid colorimetric method for the determination of isoniazid, isocarboxazid, iproniazid phosphate, phenelzine sulphate and phenylhydrazine hydrochloride is described. The method is based on the formation of ferroin, when the studied drugs react with a mixture of iron (III) and 1,10-phenanthroline, and measurement of the absorbance at 512 nm. The procedure has been successfully applied to the assay of the pharmaceutical preparations of the studied drugs and the results are favorably comparable to the official methods.

Kinetic spectrophotometric determination of some sulfur containing compounds in pharmaceutical preparations and human serum.

A kinetic spectrophotometric method was developed for the determination of carbocisteine, ethionamide, thioctic acid and penicillamine based on the catalytic effect on the reaction between sodium azide and iodine in aqueous solution. Ten to 100 microg ml(-1) of carbocisteine and ethionamide, 0.1-1 microg ml(-1) of thioctic acid and 0.01-0.1 microg ml(-1) of penicillamine could be determined, respectively, by measuring the decrease in the absorbance of iodine at 348 nm by a fixed time method. The decrease in the absorbance in the first 5 min from the initiation of the reaction is related to the concentration of the drugs. The detection limits were 0.47, 0.71, 0.018 and 9.38 x 10(-4) microg ml(-1) for the four drugs, respectively. The proposed procedure was successfully applied in the determination of these drugs in pharmaceutical preparations and human serum.

Determination of 1,4-Benzodiazepines in Drug Dosage Forms by Difference Spectrophotometry

A spectrophotometric method has been developed for the determination of seven 1,4-benzodiazepines, namely: chlordiazepoxide, diazepam, nitrazepam, oxazepam, lorazepam, temazepam and cinolazepam. The method involves reduction of the target compounds using Zn/HCl and measuring the difference in the absorbance before and after reduction. The quantities of zinc and acid required for efficient reduction were carefully studied. 1–20 μg ml−1 of the compounds could be determined with < 1% error. The method was applied successfully to the determination of these compounds in pharmaceutical dosage forms. The results were sufficiently accurate and precise and comparable to those from the official methods.

Polarographic behaviour and determination of paracetamol and salicylamide after treatment with nitrous acid

A polarographic procedure is described for the determination of paracetamol (acetaminophen) and salicylamide after treatment with nitrous acid. The different experimental parameters affecting the derivatization process and the polarographic analysis were studied. The derivatization products were found to be reduced at the dropping mercury electrode over the whole pH range in Britton-Robinson buffers. At pH 7.0, well defined diffusion-controlled cathodic waves were produced for both compounds. Plots of limiting current vs. concentration were linear over the ranges 0.05–0.75 and 0.25–1.5mM for paracetamol and salicylamide, respectively, in the d.c. mode, with minimum detectability of 2.5 × 10−6 and 1.25 × 10−5M, respectively. The procedure was applied to the analysis of some pharmaceutical dosage forms and the results were in good agreement with those obtained by official and compendial methods.

Colorimetric Determination of Some Aromatic Nitrocompounds of Pharmaceutical Interest

Abstract A simple colorimetric method for the determination of six nitro derivatives, namely: furazolidone, nifuroxime, niridazole, nitrazepam, nitrofurantoin and nitrofurazone was described. The suggested method depends upon the formation of orange to purple colour when these nitro compounds react with tetrabutylammonium hydroxide in dimethylformamide. The different experimental parameters were studied and incorporated into the procedure. The mean percentage recoveries ranged from 98.9 ± 0.3 to 100.4 ± 0.7. The proposed method was applied to the determination of certain pharmaceutical dosage forms containing the studied nitro-compounds, as well as furazolidone and nifuroxime in mixture. The results obtained were in agreement with those obtained by official and compendium methods.

Determination of Some Pharmaceutically – Important Aminoquinoline Antimalarials, via Charge – Transfer Complexes

Abstract A simple and rapid spectrophotometric method for the assay of amodiaquine hydrochloride, chloroquine phosphate and primaquine phosphate is described. The method is based on the interaction of the drug with 7, 7, 8, 8-tetracyanoquinodimethane (TCNQ) as a π-electron acceptor, forming a highly coloured stable radical anion. The molecular ratios of the reactants in the complexes as well as the experimental conditions leading to maximum charge-transfer bands have been studied. Beers Law is obeyed over aminoquinoline antimalarials concentration range of 0.4–4.0 ug.ml−1. The proposed procedure has been applied successfully to the analysis of antimalarials in their dosage forms and the results are in agreement with those of official methods.

Direct current polarographic determination of chlorprothixene and thiothixene after bromination

Abstract A direct current (dc) polarographic method is described for the determination of chlorprothixene and thiothixene after reaction with bromine. The bromo derivatives of the two drugs show a well-defined, diffusion-controlled cathodic wave; the height of the latter increases with an increase in the concentration of the depolarizers. The different experimental conditions were carefully studied and incorporated into the procedure. The proposed method was further applied to the studied compounds in dosage forms and the results obtained were compared favorably to those given by compendial methods.